1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine and a printer and, in particular, to a shutter provided in a fixing device that is applied to the image forming apparatus.
2. Related Art
FIG. 11 shows a schematic sectional view of an image forming apparatus provided with a conventional fixing device. In the figure, reference numeral 101 denotes a scanner unit having optical means for irradiating a laser beam, which is emitted according to image information, and scanning means for scanning by the laser beam and 110 denotes a process cartridge incorporating main image forming means. A photosensitive drum 103 functioning as an image bearing member, a roller charger 104 made of semiconductive rubber, a developing device 105 for carrying toner 106 onto the photosensitive drum 103 to develop an electrostatic latent image thereon and a cleaner 108 for removing waste toner from the photosensitive drum 103 are integrally incorporated in and constitute the process cartridge 110.
With the above-mentioned configuration, the photosensitive drum 103 in the process cartridge 110 is driven to rotate and the surface of the photosensitive drum 103 is uniformly charged by the roller charger 104. Subsequently, a laser beam emitted by the scanner unit 101 is irradiated on the photosensitive drum 103 via a mirror 102, whereby an electrostatic latent image is formed on the surface of the photosensitive drum 103. Then, toner is supplied to the surface of the photosensitive drum 103 to visualize the electrostatic latent image as a toner image by the developing device 105.
On the other hand, transferring materials (basis weight 64 to 216 g) 112 in a sheet feeding cassette 111 are separated piece by piece and supplied by a sheet feeding roller 113. The supplied transferring material 112 is conveyed to a pair of registration rollers 115 along upper and lower guides 114. The registration rollers 115 do not move until the transferring material 112 is supplied to them. When the transferring material 112 is supplied, its leading edge collides with the registration rollers 115, whereby skew feeding of the transferring material 112 is corrected.
Subsequently, the registration rollers 115 convey the transferring material 112 to a transferring portion in such a manner as to synchronize the end of the toner image formed on the photosensitive drum 103 with the leading edge of the transferring material 112. Further, a not-shown sheet feeding sensor is disposed in the vicinity of the registration rollers 115. The sheet feeding sensor senses a sheet passing state or jam and the length of the transferring material 112.
The transferring material 112 conveyed to the transferring portion as described above is applied a charge having a polarity opposite that of the toner by the transfer roller 107 from its back. As a result, the toner image formed on the photosensitive drum 103 is transferred to the transferring material 112. The transferring material 112 with the toner image transferred thereon is conveyed to a fixing device 118 by a conveying roller 117 and a conveying guide 116. The fixing device 118 fixes an unfixed toner image on the transferring material 112 by heat and pressure to form a recorded image thereon. Then, after the image is fixed, a conveying route is selected by a flapper 119 for the transferring material 112, which is discharged to a discharge tray 120 or 121.
Next, the fixing device 118 will be described.
The fixing device 118 is provided with a fixing roller 127 as a fixing body, a pressurizing roller 128 as a pressurizing body and a fixing inlet guide 130.
The fixing device 118 employs a central reference for conveying the transferring material 112, which has a width of A3 sheet (297 mm) as a maximum sheet passing size, with a sheet passing center of the device as a reference. The fixing device 118 of this type opens a fixing inlet shutter 123xe2x80x2 as shown by solid lines to secure a conveying path when a transferring material is conveyed. In addition, when a transferring material is not conveyed, the fixing device 118 closes the fixing inlet shutter 123 as shown by broken lines to protect a user at the time of jam treatment.
However, in the conventional fixing device 118 provided with the fixing inlet shutter 123, since an air path cannot be secured around the fixing device 118 when a transferring material is conveyed, there is no air path in the vicinity of its inlet as shown by arrows indicating a flow of air in FIG. 11. As a result, temperature in the image forming apparatus increases to cause various harmful effects. In addition, a member of a complicated structure is required to secure an air path in an apparatus main body and, at the same time, retain heat of the fixing device 118 and protect a user at the time of jam treatment and the like, which causes increase of costs.
As means for coping with this problem, Japanese Patent Application Laid-Open No. 5-333614 describes securing of an air path by providing holes in a shutter.
Incidentally, in an image forming apparatus of this type, if an opening and closing member is provided in an apparatus main body, a part of the apparatus on the opening and closing member side tends to be exposed to the open air. Thus, for example, temperature further falls in a part of a fixing device on the opening and closing member side and unevenness of temperature occurs in the fixing device.
The present invention has been devised in view of the above-mentioned drawbacks, and it is an object of the present invention to provide an image forming apparatus that prevents unevenness of temperature in fixing means while controlling increase of temperature in an apparatus main body.
Another object of the present invention is to provide an image forming apparatus comprising: fixing means for heat-fixing an unfixed image on a recording material; a shutter movable to a first position for covering the fixing means and a second position retracting from the first position; and an opening and closing member that is openable and closable with respect to an image forming apparatus main body, in which: the shutter has a plurality of holes; when the opening and closing member is open, the shutter exists at the first position and, when the opening and closing member is closed, the shutter exists at the second position; and a size of the hole on the opening and closing member side of the shutter is smaller than a size of the hole on the opposite side of the opening and closing member.
Still another object of the present invention is to provide an image forming apparatus comprising: fixing means for heat-fixing an unfixed image on a recording material; a shutter movable to a first position for covering the fixing means and a second position retracting from the first position; and an opening and closing member that is openable and closable with respect to an image forming apparatus main body, in which: the shutter has a plurality of holes; when the opening and closing member is open, the shutter exists at the first position and, when the opening and closing member is closed, the shutter exists at the second position; and an interval of the holes on the opening and closing member side of the shutter is larger than an interval of the holes on the opposite side of the opening and closing member.
Still another object of the present invention is to provide an image forming apparatus comprising: fixing means for heat-fixing an unfixed image on a recording material; a shutter movable to a first position for covering the fixing means and a second position retracting from the first position; and an opening and closing member that is openable and closable with respect to an image forming apparatus main body, in which: the shutter has a plurality of holes; when the opening and closing member is open, the shutter exists at the first position and, when the opening and closing member is closed, the shutter exists at the second position; and the holes of the shutter are provided on the opposite side of the opening and closing member side in the shutter.
Still another object of the present invention is to provide an image forming apparatus comprising: fixing means for heat-fixing an unfixed image on a recording material; a shutter movable to a first position for covering the fixing means and a second position retracting from the first position; and an opening and closing member that is openable and closable with respect to an image forming apparatus main body, in which: the shutter has a plurality of holes; when the opening and closing member is open, the shutter exists at the first position and, when the opening and closing member is closed, the shutter exists at the second position; and the hole of the shutter is rectangular.